How to Evaluate Solar Panels with 5 Key Parameters


Being careful and aware keeps you away from problems most of the time. Considering solar panels, you obviously are investing huge amounts but without proper evaluation, it is not the right choice.

The process of calculating or judging the quality of something along with the importance, value, or amount of a particular thing is known as evaluation. Similarly, evaluating solar panels is also necessary before you decide to get one. Encouraging people to shift to solar panels includes answering lots of questions and clearing out numerous doubts. One of the most common ones is how to evaluate solar panels. Some people are content with panels but confused about companies, and they want to know how to evaluate solar panel companies. If you are among them too, come find out the answer.

How to Evaluate Solar Panels?

While purchasing solar panels one should listen and understand what the supplier or installer needs to say. But having some self-knowledge is necessary to point out issues and matters that concern you. Only then can you make a fair deal that benefits you in the long run.

1. Degradation Rate

JAN23how to evaluate solar panels

This term refers to the drop in output experienced by all solar panels over time. Degradation is natural, but it does not happen for the entire solar panel system simultaneously and at the same rate. In the first year of installation, solar panels experience short-term degradation ranging somewhere between 1% and 3%. After this, each year there is an average decline of about 0.8% to 0.9% in the performance of solar panel systems.

The average lifespan of solar panels is between 20 and 40, sometimes 50 years, which means it is determined that solar panels will be producing energy for these years. However, keep in mind that the lifespan of solar panels depends firstly on the manufacturer and then on other factors like working conditions and maintenance. Therefore, lifespan is subject to change.

For example, during the 1st year solar panels worked with 100% efficiency and then faced a short-term degradation rate of 2%. This means next year their efficiency will be 98%. Since the degradation rate from next year is between 0.8% and 0.9%, after 25 years of installation, your solar panels will still be working at 78.8%.

After surpassing their rated life, solar panels will still produce energy but at a far lower rate. Annual degradation rates of solar panels by a couple of tenths of a percentage point have a significant impact on their lifetime production. Therefore, it is not something that should be neglected. Thus, considering the size of your solar system, prepare the expected production chart over time to get a realistic idea of overall performance degradation over years.

2. Durability

Another factor in how to evaluate solar panels is durability. This factor varies greatly depending on location and prevailing conditions, including other external factors. Solar panels are continuously exposed to external elements like weather, animals, water, and others. Therefore, it is necessary to ensure durability because panels not operating accurately in certain conditions will either generate less energy or ultimately fail.

Coastal areas have high winds and salt water, snow, and cold temperatures paired with cold winds are common in mountain regions. For this, you need to check whether the selected solar panels operate well in harsh weather conditions like winds, temperature fluctuations, and moisture. In areas with a moderate climate, the durability of solar panels is not influenced much.

In both situations, solar panels and their performance are adversely affected, creating a reliability issue. To avoid this, check whether the solar panels are marked with IEC 612125 mark, which is an industry-standard mark for durability.

3. Real-World Performance

Solar panels’ efficiency rating is based on lab tests or real-world scenarios. This is why it is essential to know the difference in solar panel performance in the real world vs. the lab environment. On the basis of the position and location of panels, average annual sunlight, and area-wise weather history records; solar companies should easily explain the performance difference in both scenarios. Also, if the same solar company installed the system near your location, you may ask the user also.

The projected performance of solar panels under high temperatures is another factor to consider. The efficiency of solar panels is affected to a certain extent under high temperatures. This could be a matter of concern if you live in hotter regions with frequent high temperatures of about 80° Fahrenheit or above.

Therefore, it is better to account for performance fluctuations in your production calculations. With this, your expectations of energy generation will be accurate, and a payback estimate could be prepared accordingly.

4. Solar Panel Efficiency

JAN23how to evaluate solar panelsThis is another factor to help you how to evaluate solar panels. The percentage of solar energy absorbed by photovoltaic cells and converted into electricity is the conversion efficiency of a photovoltaic, solar, or PV cell. The efficiency of solar panels is determined by the type of solar panels, namely monocrystalline, polycrystalline, and thin film solar panels.

a) Monocrystalline panels: These are made from single silicon crystal cut into wafers thus making them the most efficient with an average efficiency rating between 15% and 20%. Due to this, these panels are costly, which is their only drawback.

b) Polycrystalline panels: Made from multiple silicon crystals that are melted and poured into molds and then cut into wafers, making them slightly less efficient than monocrystalline solar panels. With an average efficiency rating between 15% and 17% these solar panels are affordable and give optimum performance.

c) Thin film panels: These panels are made from silicon, Copper Indium Gallium Selenide (CIGS), and cadmium telluride (CdTe) and have the least efficiency rating between 8% and 10%. Due to low material costs these panels are not costly.

Other factors determining the type of panels depend on energy requirements, available square footage space on the roof, and the physical size of solar panels to be installed.

With a glimpse of types of solar panels, you can decide what matters: efficiency, cost, or space. Because with less space you cannot install many panels thus most efficient panels are preferred for delivering the required amount of energy.

However, fewer panels also mean lower installation costs plus you always have the leverage to add panels in the future if required. Do not make self-changes here and there to cater to your energy requirements because it hampers the overall performance of the system. Take in-depth information about the complete analysis of your solar panel system.

5. Warranty Coverage

Solar panels usually are not problematic, but nothing is completely perfect similarly solar panels or their components too, have some defects. All solar panels are covered under 2 types of warranties:

  • The product warranty covers solar panels against defects.
  • The power warranty covers the minimum promised power rating for solar panels.

These warranties are an essential factor in how to evaluate solar panels. Both warranties may be for the same period, 25 years combined, or for different periods like a 10-year warranty for the product and a 25-year power warranty. This depends on the supplier and your location. Also, the services required for replacing underperforming or defective panels may or may not be included in these warranties.

Question to be asked relating to warranties-

  • How does the company handle warranty orders?
  • What is a reasonable timeline expectation?
  • What will the customer and company be responsible for?
  • Will you be paying for shipping or replacement services?
  • Does it come with technical support?

Before the time to replace or repair comes, it is better to have answers to all these questions. This will ensure smooth navigation of a warranty claim and the problem will be fixed as soon as possible. After this, let’s learn about solar panel evaluation factors.

Also Read: How Solar Panels Work Step By Step

How to Test Solar Panel Evaluation Factors?

JAN23Test Solar Panel
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Before you purchase the panels, it is essential to check the panels for certain tests and certificates. Here is how to test solar panel evaluation factors.

1. Certification

It is proof that manufacturers are producing solar panels as per industrial standards. You should ask for PV product certifications while making the purchase. A certified solar module is the standard for the profitability and security of your invested amount.

Some common certifications issued by the International Electrotechnical Commission (IEC) and European Standards (EN) are mentioned below.

  • IEC 61215 / EN 61215, IEC 61215 Ed. 2, IEC61646, IEC 61730 / EN 61730, IEC 60364-4-41, IEC 62108, and IEC 61701

2. Flash test

This is a common test among others like I-V (current-voltage) data measurement test, and sun simulation test. During a flash test, solar modules are exposed to a short 1 ms. to 30 ms. flash of light with 100 mW. per square centimeter brightness from a xenon-filled arc lamp. The output spectrum of this lamp is kept as close to the sun as possible, then a computer collects the output data and compares it with a reference sheet of the solar module. The power output of this reference sheet is calibrated to standard solar irradiation. The result of the flash test is the number printed on the label at the back of the module which is also an important factor in how to evaluate solar panels.

Also See: How to Test a Solar Panel With a Multimeter?

3. Standard Test Conditions

Parameters for testing solar modules are measured at standard test conditions (STC). At a specific temperature of 25 ׂ °C, the irradiance of 1000 W per meter square, and an air mass of AM 1.5 spectrum are specified at STC. Solar panels correspond to these conditions on a clear day with a spectrum of sunlight incident and surfaces facing the sun at a titled angle of 37°. All this takes place when the sun is 41.81° above the horizon. This situation resembles the sunny noon during spring and autumn equinoxes basically in the continental United States.

4. Visual Inspection

Visual inspection is another one of the solar panel evaluation factors. A certified testing agency performs the visual inspection of each solar panel. They carefully look for defects like glue marks, montage frames, scratches, and other similar deviant issues. A panel with such visible defects means it has not been visually tested.

Also Read: How to Test a Solar Panel Without a Multimeter?

What Common Defects to Notice in Solar Panels Through Standard Test Conditions?

Some common defects and points highlighted by standard test conditions to look out for while purchasing solar panels are as follows:

  • Uneven or excess glue marks or glue marks on glass
  • Lower Fill Factors (FF) than mentioned in the requirements
  • Due to poor sealing gap between the glass and frame
  • Scratches on glass or frame
  • Lower output than mentioned in the datasheet

Other defects are dirt marks on the panels, gaps in corner of the photovoltaic frame, along with poor quality labels with solar panels that do not meet positive tolerance requirements.

Also See: BIPV vs BAPV

What Are Standard PV Testing Parameters?

With a flash test, solar panels are tested for the following parameters.

1. FF (%): It is defined as the maximum power produced at MPP divided by the product of ISC and Voc. Usually, the fill factor is less than 1 and is preferably used because quick measurement of conversion efficiency is difficult.

2. Imp (A): This is the number of amperes delivered by modules at the maximum power point. It is known as the second current rating, also known as current at maximum power point (Imp). This is the second important level in which the current rating is divided.

3. ISC (A): How to evaluate solar panels with ISC? This is rated at 2 important levels, and it is the first one is known as Short Circuit Current (ISC) which is the amount of current supplied by photovoltaic modules into a dead short.

4. Pm (W): It is the specific point on the power curve where the product of Amps times volts yields the greatest wattage. It is also known as maximum power or maximum power point. The wattage of the module is rated at voltage and current at this point. The entire voltage and current range are considered to calculate this.

5. Rubbing test: This test is for the label at the back of solar panels ensuring whether it will still be readable after 25 years. Rub the label with a mix of alcohol and water. It is essential as the serial number is directly linked to the guarantees of solar panel manufacturers.

6. VMP (V): It is also a second voltage rating known as Voltage at Maximum Power point (VMP) and at this point a solar module puts out the most power. All voltage measurements are made with highly accurate voltmeters at electrical terminals mounted at the back of modules.

7. VOC (V): It is the first voltage level at which PV modules are rated. Known as open circuit voltage is measured when the module is disconnected from any load.

Also See: What is Light Induced Degradation?

How to Evaluate Solar Panel Companies?

JAN23How to Evaluate Solar Panel Companies?
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With the increasing number of solar companies in the market, it is difficult to decide which one is the best. Now the question arises of how to evaluate solar panel companies. For this, here is a brief description of things to consider while evaluating solar panel companies.

1. Years of Expertise and Business

Photovoltaic cells were made in 1954 but not every solar company began soon after that. But a good solar company must have at least an established record of 10 years. This time period shows that the brand is capable of making and holding its position in the market on the basis of its products and services. There have been solar companies in the market for more than 30 to 50 years and these involve premium brands LG, Panasonic, and Q Cells. This is one of the factors in how to evaluate Solar Panels Company.

However, taking past records into consideration is important but looking for future existence is equally important. If a company goes off the market a couple of years after the date you installed the solar modules, where will you do the warranty claim?

2. Research, Reputation and Reviews

Getting a solar panel system is a big decision and a heavy one for your pocket. Therefore, research thoroughly for the solar companies and take your time for this. Ensure online and offline reviews of whether a solar company is reputable and has a good track record. Ask out other nearby customers of the same solar company, if possible, for a more reliable review.

3. Compatible

Different types of solar panel systems are distinct. Check whether the solar company provides solar panels compatible with your home and business because not every system works well with every roof type.

Also See: 6 Best Roof Material For Solar Panels

4. Financial Backing

Since solar panel installation is expensive, make sure that the selected solar company has strong financial backing. A company ensuring you accurate financing for solar panel installation guarantees you better after-sales services. You can rest assured that the company is reliable.

5. Licenses, Certifications, and Affiliations

Solar companies and installers must have the necessary insurance and license for operation. Note: Insurance policies and certification standards may vary depending on location. In terms of additional industry certifications, a popular one is the North America Board of Certified Energy Practitioners (NABCEP) Solar PV Installation Professional Certification. Several solar companies have multiple NABCEP-certified lead installers.

Also See: What is Solar Net Metering?

6. Installation Timeline

Not every solar company is instantly available as per your available schedule. The installation process is also dependent on the availability of installing crews and project managers. If you work as per schedule, then search for the one according to it or talk to the installer to manage things accordingly.

Well, while referring to and considering various factors in how to evaluate solar panels you will surely make better decisions. After deciding the best panel for your house or office, it is time to decide on a solar company. How to evaluate solar panel companies? The answer to this also includes a number of factors to check out.

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